1. Field of the Invention
The present invention relates to an inkjet image forming apparatus. More particularly, the present invention relates to a method and apparatus for an inkjet image forming apparatus which can compensate for image degradation caused by malfunctioning nozzles, and an inkjet image forming apparatus using the same.
2. Description of the Related Art
An inkjet image forming apparatus forms images by ejecting ink from a printhead, which is placed a predetermined distance from a print medium and reciprocally moves in a direction perpendicular to a transferring direction of the print medium. Such an inkjet image forming apparatus is referred to as a shuttle-type inkjet image forming apparatus. A nozzle unit having a plurality of nozzles for ejecting ink is installed in a printhead of the shuttle-type inkjet image forming apparatus.
Recently, a printhead having a nozzle unit with a length corresponding to the width of a print medium has been used to obtain high-speed printing. An image forming apparatus operated in this manner is referred to as a line-printing-type inkjet image forming apparatus. In the line-printing-type inkjet image forming apparatus, a printhead is fixed and only the print medium is transferred. Accordingly, a driving device of an inkjet image forming apparatus is simple and high-speed printing can be performed.
FIG. 1 shows printing patterns obtained when the nozzle of a conventional inkjet image forming apparatus malfunctions. FIGS. 2A through 2D are pixel images for explaining a conventional method of compensating for a malfunctioning nozzle of the conventional inkjet image forming apparatus.
Referring to FIG. 1, the inkjet image forming apparatus forms an image by ejecting ink I from nozzles 82 formed in a nozzle unit 80 onto a print medium. When a nozzle 84 malfunctions, the malfunctioning nozzle 84 irregularly ejects ink I so that a missing line appears on the print medium, as illustrated in FIG. 1. That is, when a malfunctioning nozzle 84 exists among the plurality of nozzles 82, a missing line, such as a visible white line, will appear on the print medium because the malfunctioning nozzle irregularly ejects ink. Thus, printing quality is degraded by the presence of the missing line.
A method of compensating for image quality degradation due to a malfunctioning nozzle is disclosed in U.S. Pat. No. 5,581,284, from which FIGS. 3 through 6 are reproduced herein as FIGS. 2A through 2D, and which is incorporated herein by reference.
U.S. Pat. No. 5,581,284 discloses a method of compensating a malfunctioning nozzle in an inkjet image forming apparatus. The malfunctioning nozzle indicates a bad or non-droplet ejecting nozzle. When, for example, a black ink nozzle 63 is identified as malfunctioning, ink droplets of other colors, that is cyan, magenta, and yellow, are sequentially ejected to a region in which the malfunctioning nozzle should have ejected black ink. These processes are illustrated in FIGS. 2B, 2C, and 2D.
As described above, the black color can be represented by printing the cyan, magenta, and yellow ink droplets at the same location on the print medium where black should have printed, and the represented color is called “process black” or “composite black.” Although this method of compensation is useful to compensate for malfunction of a nozzle ejecting black ink, it is not possible to compensate for malfunction of nozzles ejecting other colors. Further, when one of the nozzles used for compensation malfunctions, other colors such as red (yellow+magenta), green (cyan+yellow), or blue (cyan+magenta) are printed. Thus, printing quality is deteriorated. Hence, there is a need for compensation of malfunctioning nozzles to improve the image quality.